Piezoelectric heart assist apparatus

ABSTRACT

An implantable piezoelectric heart assist apparatus generates pressure waves of approximately the same amplitude and frequency as the natural heart. The apparatus includes a brass support sandwiched between piezoelectric ceramics to form a piezoelectric bender. The bender compresses a tube which is sutured into the descending thoracic aorta. The bender is loaded at one end to change its resonant frequency and, upon application of a driving signal, the bender oscillates to generate pressure in the thoracic aorta.

United States Patent [191 Williams, Jr. et al.

[111 3,857,382 [451 Dec.3'1, 1974 PIEZOELECTRIC HEART ASSIST APPARATUS Inventors: Maryon J. Williams, Jr., Augusta,

' Ga.; Walter Welkowitz, Metuchen; Sylvan Fich, Edison, both of N.J.; Dov Jaron, Detroit; Adrian Kantrowitz, Pontiac, both of Mich.; Donald A. Molony, Vienna, Austria Sinai Hospital of Detroit, Detroit, Mich.

Filed: Sept. 10, 1973 Appl. No: 395,799

Related US. Application Data Continuation-in-part of Ser. No. 301,553, Oct. 27, 1972, abandoned.

Assign'ee:

US. Cl. 128/1 D, 3/DlG. 2, 128/346, 251/9, 417/322 Int. Cl. A61m 01/03, A61f 0l/24 Field of Search 128/1 D, 214 R, 273, 346; 3/1, DIG. 2; 251/9; 417/322, 478

References Cited UNITED STATES PATENTS 1/1960 DiVette 128/346 3,361,067 1/1968 Webb ..'417/322 OTHER PUBLICATIONS Myers et al., Amer. Jour.. Med. Elect., .Oct.-Dec., 1964, PP. 233-236.

Primary ExaminerDalt0n L. Truluck Attorney, Agent, or Firm-Cullen, Settle, Sloman & Cantor 5 7 ABSTRACT An implantable piezoelectric heart assist apparatus generates pressure waves of approximately the same amplitude and frequency as the natural heart. The ap- 6 Claims, 9 Drawing Figures P452054 ECTR/c BEA/05R PIEZOELECTRIC HEART ASSIST APPARATUS CROSS REFERENCE TO RELATED APPLICATION This is a continuation-in-part of our United States patent application Ser. No. 301,553 filed Oct. 27, 1972 now abandoned.

BACKGROUND OF INVENTION National Science Foundation.

This invention relates generally to heart assist devices and, more particularly, to heart assist-devices operating in a counter-pulsation mode.

Heart assist devices operating in a counter-pulsation mode have been previously developed'TechnicaI problems arising with these prior art devices include the large'amount of power. necessary for operation, the inability to generate sufficient pressures in vivo, and low efficiency.

The use' ofpiezoelectric transducers in heart assist devices is also known. One problem with prior piezoelectric transducers applied to heart assist devices is their high natural resonant frequency. Additional problems in the 'prior piezoelectric devices include the requirement that valves, pistons or levers be included.

SUMMARY OF THE INVENTION The invention herein relates to an improved implantable piezoelectric heart assist device including a fluid path, adapted to be surgically connected to the bloodstream and piezoelectric means for alternately compressing and releasing the fluid path to generate sinusoidal pressure waves in the bloodstream. The piezoelectric means includes a brass support which is fastened at one end .to form a cantilever and is sandwiched between piezoelectric ceramics to form a piezoelectric bender. In one embodiment a single bender is provided.

It is yet another object of the present invention to provide an improved piezoelectric heart assist apparatus eliminating the need for valves, pistons and other similar mechanical elements.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing objects of the present invention, together with other objects and advantageswhich may be attained by its use, will become more apparent upon reading the following detailed description taken in conjunction with the drawings. I

In the drawings, wherein like numerals identify corresponding parts:

FIG. 1 is an illustration of the human heart;

FIG. 2 is a perspective illustration of single piezoelectric bender heart assist apparatus according to the present invention;

FIG. 3 is a driving circuit for the piezoelectric bender of the present invention; a

FIG. 4 is a schematic illustration of the use of the heart assist apparatus without bisecting or severing the thoracic aorta;

FIG. 5 is a schematic illustration of the use of the heart assist apparatus with the thoracic aorta severed;

FIG. 6 is a top plan view of a double piezoelectric bender heart assist apparatus according to the present invention;

FIG. 7 is a front elevation view taken in the direction of arrows 77 of FIG. 6; I

FIG. 8 is an end elevation view taken in the direction of arrows 88 of FIG. 6; and

FIG. 9 is an enlarged, partially exploded perspective illustration of part of the apparatus of FIGS. 6-8.

DETAILED DESCRIPTION OF THE INVENTION -mounted in a housing (not shown), including a center brass support 32 and two piezoelectric ceramic means 34 bonded to either side of the brass support 32 to form a sandwich.

The brass support measures 5.75 X 2.75 inches with a thickness of 0.008 inch. Three ceramic strips are bonded-to each side of the brass support. The strips measure 30 X 0.9 X 0.005 inch each, and are a lead zirconate titanate (G I278) manufactured by Gulton lndustries, Inc. of New Jersey.

. The piezoelectric bender of FIG. 2 is clamped at one end 36 to form a cantilever and the free end is loaded with a mass 38 tochange the resonant frequency ofthe bender. The piezoelectric bender is clamped to a support 40', and a tube 42, which may bemanufactured of segmented polyurethane or any other blood compatible material, passes between the piezoelectric bender and support member 40. The apparatus may be surgically implanted in the chest cavity, hence the requirement of compatible materials is obvious.

Referring to FIG. 3, the driving circuit of the present invention includesa pulse generator 44 which supplies a pacingsignal to the heart. The pulse generator also provides a delayed output which serves as an input to a square wave generator 46. The output of the square wave generator is coupled through a resistance network 48 to the piezoelectric bender,

The operation of the heart assist device is based upon the characteristic of a piezoelectric bender. That is, when a voltage is applied across a piezoelectric bender which is clamped at one end, the bender responds with an oscillatory deflection at the free end. The resonant frequency of the bender, dependent upon the size and mass of the bender, may be adjusted by the inclusion of an additional mass such as mass 38 of FIG. 2.

EXAMPLE I Various in vivo experiments were undertaken with mongrel dogs. With reference to FIG. 5, a first example included use of the piezoelectric apparatus assisting the left ventricle with the thoracic aorta 30 bisected and the polyurethane tube sutured or clamped to both ends of the thoracic aorta. Ventricular failure in the animal was surgically induced. The driving system was a 200- volt peak-to-peak square wave although it is recognized that a sine wave could be utilized since the oscillatory motion of the piezoelectric bender produces a sinusoidal output. Mass 38 was 330 grams.

EXAMPLE ll EMBODIMENT OF FIGS. 6-9

To provide greater pressure on the tube 42 and to reduce the sensitivity to spatial orientation, the embodiment of FIGS. 6-9 provides a double cantilever bender apparatus. The apparatus includes a frame or housing 52, which may be made of clear plastic or plexiglass and includes two opposed side walls 54, each having a central aperture 56.

A connector 58 which may be manufactured of teflon, plastic or other surgically compatible material, is inserted in each aperture 56. The connector has a flange 59, which may be manufactured of brass, and which projects inward of the housing 52 and fits inside a bearing 60. The bearing 60 is a dry ball bearing unit having a stationery inner shaft and a rotating outer shaft.

Rocker arms 62, 63 having central openings 64 are mounted on the outer shaft of the bearing 60 for oscillation.

A first cross-support 66 connects the end of the first rocker arm 62 with the end of the second rocker arm 63. A second cross-support 67 connects the remaining end of the rocker arm 62 with the remaining end of the rocker arm 63. Each cross-support is secured to a mass 68 by means of screws 70 which are threaded through the cross-support and are adjustable to move the mass radially inward and outward with respect to the center of the opening 64 in the rocker arm. Thus, the rocker arm operates with the two masses 68 as a counter balance.

The embodiment of FIGS. 6-9 includes two piezoelectric bender elements 72 each having a central brass support (as in FIG. 2) and each including a brass plate 74 at one end to provide additional stiffness. Each bender element is configured as a cantilever with the mass 68 operably loading the free end. Each bender element has a plurality of apertures 76 at a fixed end 78 which is secured by bolts 80 to the frame or housing 52. The cantilever support further has a plurality of slits 82 at the free end 84.

As in the first embodiment, each bender 72 has a plurality of piezoelectric ceramics 34 bonded thereto. In

this second embodiment, the central brass support measures 5.25 inches X 0.95 inch 0.004 inch and i each ceramic measures 3.0 inches X 0.3 inch X 0.008 inch. Each bender 72 comprises three adjacent ceramics on each side of the support. Thus, the total dimension of the ceramic on each side of the brass support is 3.0 inches X 0.9 inch X 0.008 inch.

At the free end 84 of each bender is a U-shaped brace 86 having opposed legs 88. Each leg 88 has an elongated slot 90 having a longitudinal axis parallel to the axis of the central brass support 74. At each end of the apparatus is a pin 92 which extends from the first rocker arm 62 through the slots 90 to the other rocker arm 63. By this pin and slot connection, each mass 68 loads one of the piezoelectric benders 72 for adjusting resonant frequency.

As in the first embodiment, the principles .of operation are the same. The application of a driving voltage across the bender elements causes each piezoelectric cantilever to oscillate about its fixed end and thereby generate the pressure waves within the tube 42. The mass may be utilized to adjust resonant frequency and the central brass support, in each embodiment, may be utilized as a fine adjustment of resonant frequency by slight sliding ofthe brass with respect to the individual slots 82 to thereby change the lever arm of the support with respect to the fixed end.

As in the first embodiment, the entire flow of blood may be through the tube 42 or, a T adapter may be utilized with pressure waves propagating into the main bloodstream.

' The use of the counter-balanced rocker arms 62 and 63 provides for oscillation about the central axis 96 of the tube 42. Each bender element oscillates or deflects at its fixed end 84. To compensate for the different axes 'of motion and thereby prevent binding of the central brass supports, the slot 90 in the legs 88 are utilized- Furthermore, a copper plate 98 may be pivoted at the fixed end of the brass support to distribute the flexing force of the cantilever evenly across the tube 42.

RESULTS The expected results in a left ventricular heart assist device of this nature are a decrease inthe systolic pressure and an increase in the diastolic pressure. These expected results for the single bender device were obtained as reported by us at the 24th Annual Conference first embodiment, the fundamental component of the pressure generated by the device in the carotid artery was 15 mmI-Ig peak-to-peak. This was approximately equal to the fundamental component of the pulse pressure in the carotid artery with the device off. The typical counter-pulsation pressure wave form was readily noted in the aortic pressure curves. A typical power consumption of one watt was noted for these experiments.

The results using the double bender or double cantilever apparatus were also as expected. It was found that coronary-arterial flow was increased from 6 to 20 percent in various experiments and the in-phase fundamental aortic pressure can be decreased from 23 to 10 mmHg peak-to-peak based upon the location of the bender along the aorta and the delay setting on the pulse generator 44. Again, typical power consumption of one watt was noted.

In each embodiment, the same driving circuit was utilized.

It should be appreciated that the present heart assist principles may be employed in a device placed in parallel with the heart to bypass any of the chambers of the heart. The principles may also be utilized to bypass the heart entirely.

The foregoing is a description of the concepts of the present invention and of several embodiments which have operated successfully. The description should not be read in a restrictive sense but only as describing the underlying concepts of the present invention. The invention may be further developed within the scope of the following claims.

What is claimed is: 1. Apparatus for providing mechanical assistance to a heart by generating pressure waves in the blood a tubular fluid path of resilient material adapted to be surgically connected to the bloodstream; piezoelectric means for alternately compressing and releasing said tubular fluid path and for generating sinusoidal pressure waves in said tubular-fluid path in response to a driving signal; and a frame; said piezoelectric means including at least two piezoelectric bender means each bender means having a central support and a piezoelectric ceramic bonded thereto, each bender means configured as a cantilever with one end fixed to said frame and the other end free, and having a mass operably loading the free end thereof to provide a predetermined resonant frequency; a whereby upon application of said driving signal, each piezoelectric bender means resonates at a frequency in the range of the heart frequency to generate pressure waves in said tubular fluid path thereby increasing the mean arterial bloodflow.

piezoelecoscillation therein about the axis of said tubular U which slots are parallel to the longitudinal dimension of the cantilever, and

.an elongated pin positioned through said slots and fixed in the ends of said arms;

whereby the resonating of said supports is coupled through the slot and pin to oscillate said arms, and

the arm and support move about different axes Without binding.

4. The apparatus of claim 2 wherein said tubular fluid path has means connectible to the bloodstream at two different locations whereby all the blood passes through said tubular fluid path between said piezoelectric cantilever means and said base.

5. The apparatus of claim 2 wherein said tubular fluid path has means connectible to the bloodstream at one surgical location and pressure waves are propagated ezoelectric cantilever means. 

1. Apparatus for providing mechanical assistance to a heart by generating pressure waves in the bloodstream, the pressure waves being introduced in the bloodstream so that diastolic pressure is increased; the apparatus comprising: a tubular fluid path of resilient material adapted to be surgically connected to the bloodstream; piezoelectric means for alternately compressing and releasing said tubular fluid path and for generating sinusoidal pressure waves in said tubular fluid path in response to a driving signal; and a frame; said piezoelectric means including at least two piezoelectric bender means each bender means having a central support and a piezoelectric ceramic bonded thereto, each bender means configured as a cantilever with one end fixed to said frame and the other end free, and having a mass operably loading the free end thereof to provide a predetermined resonant frequency; whereby upon application of said driving signal, each piezoelectric bender means resonates at a frequency in the range of the heart frequency to generate pressure waves in said tubular fluid path thereby increasing the mean arterial blood flow.
 2. The apparatus of claim 1 wherein said piezoelectric means fUrther includes: an arm mounted transversely of said tubular fluid path for oscillation in said frame about the axis of said tubular fluid path; said arm having one of said masses secured to each end thereof to form a counterbalance; whereby upon application of said driving signal, said central supports resonate to oscillate said arm to compress said tubular fluid path between said supports for generating said pressure waves therein.
 3. The apparatus of claim 2 and further including: two arms mounted on opposite sides of said frame for oscillation therein about the axis of said tubular fluid path; each central support resonating about an axis distinct from the axis of said tubular fluid path; said central support including a U-shaped brace on its free end, said brace having slots in the legs of the ''''U'''' which slots are parallel to the longitudinal dimension of the cantilever, and an elongated pin positioned through said slots and fixed in the ends of said arms; whereby the resonating of said supports is coupled through the slot and pin to oscillate said arms, and the arm and support move about different axes without binding.
 4. The apparatus of claim 2 wherein said tubular fluid path has means connectible to the bloodstream at two different locations whereby all the blood passes through said tubular fluid path between said piezoelectric cantilever means and said base.
 5. The apparatus of claim 2 wherein said tubular fluid path has means connectible to the bloodstream at one surgical location and pressure waves are propagated into the main bloodstream.
 6. The apparatus of claim 2 wherein each mass is radially adjustable on said arm with respect to the axis of rotation for adjusting the resonant frequency of said piezoelectric cantilever means. 